The present invention relates a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device including an electrode having a high aspect ratio.
In a manufacturing process of a semiconductor device, a pattern is formed in a film being processed, such as an interlayer dielectric disposed on a semiconductor substrate, by a dry etching method using a resist mask. As the degree of integration of semiconductor devices increases, finer patterns are formed. Accordingly, a dry etching method has been developed so as to achieve a higher degree of precision corresponding to those finer patterns.
As the degree of integration of semiconductor devices increases, a processing depth tends to increase while a processing area that is processed by dry etching is reduced. Particularly, a “high-aspect-ratio” pattern (i.e. cylindrical hole), which has a high ratio of a processing depth to a processing area, needs to be formed as a hole pattern for forming lower electrodes of capacitors.
However, as an aspect ratio becomes higher, a dry etching method finds difficulty in processing. This is because a sputtering effect of an ionized etching gas is used to dry-etch a silicon oxide film (SiO2), which has widely been used as a material for an interlayer dielectric. Specifically, as a pattern has a higher aspect ratio, more kinetic energy is lost because more ions collide with sidewalls by the time they reach the bottom of the pattern. As a result, the sputtering effect obtained by ions that have reached the bottom of the pattern is also lessened. Thus, a dry etching method finds difficulty in processing as an aspect ratio becomes higher. Furthermore, when a silicon oxide film is dry-etched, fluorine radical is generated from an etching gas including fluorine (F). Because fluorine radical provides isotropic etching, side-etching occurs locally in a sidewall of a hole. Thus, the hole is formed into a bowing shape. If the side-etching proceeds, then adjacent hole patterns may be brought into contact with each other. It is difficult to avoid those phenomena in a dry etching process of a silicon oxide film.
In order to avoid the above phenomena, use of an amorphous carbon film instead of a silicon oxide film has been proposed (see, e.g., JP-A 2006-135261). An amorphous carbon film is hereinafter referred to as an AC film.
In a dry etching process of an AC film, an etching gas being used primarily contains oxygen (O2), and etching is conducted primarily by radical reactions. This etching can be conducted irrespective of attenuation of the kinetic energy of ions. Furthermore, a pattern having a high aspect ratio can be formed with high accuracy by using an additive gas to suppress occurrence of bowing due to radical reactions.